What happen to the current and voltage of a battery if it in connected in series and parallel?

assuming the batteries are the same:

if you connect + to + and - to - the line out will be the same volts as one battery (parallel)

if you connect + to - and - to + (series) the line out will be the sum of all the batteries in series Do not connect batteries together in either configuration unless they are the same size and rating Observe all safety precausions when handling batteries